1. Field of the Invention
The present invention relates to a data processing system including different throughput access sources, and more particularly to a control means, introduced in the system, for carrying out an access from a plurality of access sources having different throughputs to a main storage unit in a consecutive block access mode.
Recently, along with an increase in scale of data handled in an information processing system, a scale of an access to the main storage unit in the system has also become large. In addition, there is a recent tendency for the main storage unit to be accessed by a variety of access sources, such as a vector processing unit, an extended storage unit and the like, other than usual access sources, such as a scalar processing unit, an input/output (I/O) processor, and the like. Under the circumstance mentioned above, a need has arisen for accessing the main storage unit by accessing addresses which specify each consecutive long addresses thereof. In relation to the consecutive long addresses, which are hereinafter is referred to by the term "consecutive block access" which means that each memory area specified by consecutive addresses is divided into a plurality of blocks and the thus divided blocks are accessed sequentially. A typical usual working throughput therefor is hereinafter referred to as a "throughput of consecutive block access".
In the above-mentioned data processing system including different throughput access sources, when a certain access source having a large throughput starts accessing the main storage unit in the consecutive block access mode while another access source having a small throughput has already started accessing the main storage unit in the consecutive block access mode, there is a high probability that a conflict in access will occur between both access of the sources at the same addresses of the main storage unit.
In the case of such conflict, the access source having the large, throughput has to wait until the access to the main storage unit is completed by the other access source having the small throughput, since, in the exemplified case, the former access source having the large throughput starts the access after the access carried out by the latter access source having the small throughput. This apparently reduces the total throughput of the related data processing system, and accordingly, it has long been hoped to improve the data processing efficiency.
2. Description of the Related Art
In the prior art, one proposal for improving data processing efficiency has been disclosed in a European Patent Application (Applicant FUJITSU LIMITED) with a publication number 0,215,621 (A2) published on Mar. 25, 1987. According to the prior art, as depicted in FIG. 3 of the publication, the consecutive block accesses are performed intermittently so as to create nonaccess periods along the line of the consecutive block accesses. Thus, continual consecutive block accesses can cross the intermittent consecutive block accesses without conflict by passing through the aforesaid nonaccess period. The prior art, however, has a disadvantage that the aforesaid intermittent consecutive block accesses per se exhibit relatively low efficiency throughput.